1. Field of the Invention
The present invention relates to a fluid loading apparatus for use in, in particular, loading and unloading fluid from a tanker to an installation on land, and, more particularly, to a driving mechanism for driving the inboard arm and the ouboard arm of the apparatus.
2. Description of the Prior Art
It is desired for the fluid loading apparatus to make the swing range of an inboard arm thereof with respect to a stand pipe, to the top of which one end of the inboard arm is rotatably connected and of an outboard arm thereof with respect to the inboard arm, to the other end of which one end of the outboard arm is rotatably connected, as wide as 180.degree., respectively.
As typical driving devices for the fluid loading apparatus, which satisfy the above mentioned requirement, there are two systems, in one of which the inboard arm is rotated with respect to the stand pipe by pulling a looped wire rope or chain by means of a hydraulic motor provided in the loop and in the other of which the inboard arm is rotated with respect to the stand pipe by a hydraulic cylinder which drives the inboard arm directly. In these typical conventional systems, however, the maintenance of the wire rope or chains in the first system is very difficult because the fluid loading apparatus must be installed in salty atmosphere on shore and there is a need of frequently providing a rust-resisting lubricant thereto. Furthermore, due to the elastic elongation of the wire rope, time lags may be introduced in starting and stopping rotations of the arms, resulting in some difficulty in operation. Although the second system has no disadvantages inherent to the first system, the swing angle can not be practically widened up to 180.degree..
Describing the conventional apparatus of these types in more detail, an example of the firstly mentioned conventional fluid loading apparatus is shown in FIG. 1.
In FIG. 1, a stand pipe 10 is provided having a lower end connected to a pipeline providing a fluid passage to a suitable reservoir on land on a fundamental structure such as a seaberth or pier. The upper end of the stand pipe 10 is connected to the inner end of an inboard arm 14 by a hollow three-dimensionally rotatable joint 12. To the outer end of the inboard arm 14, the inner end of an outboard arm 18 is connected by a hollow rotary joint 16 which is rotatable in a vertical plane. A hollow, three-dimensionally rotatable joint 20 is connected to the outer end of the outboard arm 18. The inboard arm 14 has an extension member 22 which extends from the inner end thereof and acts, together with a counterweight 24, as a balance arm. The hollow rotatable joints 12, 16 and 20 allow the fluid loading apparatus to provide a three-dimensional movement of a mainfold flange (not shown) provided on a tanker, which is connected to the outer end of the rotatable joint 20 relative to the land. A pair of wheels 26 and 28 are employed, between which a looped wire 30 is stretched. The wheel 26 is fixed to the joint 12 and the wheel 28 is rotatably connected to the inboard arm 14. The wire rope 30 is driven by an hydraulic cylinder 32 to thereby swing the inboard arm 14 with respect to the stand pipe 10. As regards the swing between the inboard arm 14 and the outboard arm 18, a pair of wheels 26' and 28', a wire rope 30' and a hydraulic cylinder 32' are used together with another pair of wheels 34 and 36, a wire rope 38 and a counter weight 40. The wheel 26' is rotatably mounted on the extension 22 of the inboard arm 14 and fixedly connected to the wheel 34 and the weight 40. The wheel 36 is fixed to the inner end of the outboard arm 18 and rotatable with respect to the outer end of the inboard arm 14. The apparatus of this type can provide an inner angle between the inboard arm and the stand pipe up to 180.degree.. However, it is required to supply a rust resisting lubricant to the wire rope frequently for maintenance thereof and to check the breaking of filaments of the wire. Further, there is a problem that the wire is possibly elongated by the load exerted thereon as mentioned previously, causing the mechanical balance to be broken.
An example of the secondly mentioned conventional apparatus is shown in FIG. 2, in which a hydraulic cylinder 44 is rotatably secured to an extension of the inboard arm 14 and a top or end of a piston rod 46 which projects from cylinder 44 is connected to an arm 42 fixed to the joint 12. An arm lever 50 is fixedly secured to the inner end of the outboard arm 18. An outer balance arm 48 having a counterweight 54 at one end thereof is rotatably secured to the rear end portion of the extension portion 22' of the inboard arm 14 and a free end of the arm lever 50 is connected to the free end of the outer balance arm 48 by a connecting rod 52 so that, when the outboard arm 18 moves with respect to the inboard arm 14, the outer balance arm 48 is moved through the arm lever 50 and the connecting rod 52 to maintain the balance therebetween.
This fluid loading apparatus has an advantage that the maintenance is relatively easy because of the use of the connecting rod instead of the wire rope etc. However, since the load exerted on the piston rod 46 and/or the connecting rod 52 may be unreasonably increased because the length of moment arm becomes very short when the angle between the associated members becomes large, a sufficiently large inner angle (more than approximate 160 degrees) between the inboard arm and the stand pipe and/or the two arms can not be obtained and so the operation range is relatively narrower. Further, since when the outboard arm is retracted inwardly, a compressive force is exerted on the connecting rod 52, the cross sectional area of the connecting rod and hence the buckling force thereof must be sufficiently large.
Although this structure provides an advantage in maintenance, the practical rotation angle of the inboard arm 14, about the center 0 is 120.degree. at most as shown in FIG. 3. In order to achieve a wider rotation range, it is necessary to use a powerful hydraulic pressure cylinder having a longer stroke. This is not practical.